toolchain-external: add hashes for musl toolchains

Add hashes for all musl toolchains, including the ones that we
currently don't support (arm hf, sh4, x86_64-x32).

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>